X-Ray Detection System

The present application claims priority under 35 U.S.C. § 119 to European Patent Application No. 24207236.1, filed Oct. 17, 2023, the entire contents of which is incorporated herein by reference.

One or more example embodiments relates to an X-ray detection system comprising a signal processing device comprising input means for receiving an input signal based on detected X-ray photons, signal processor for generating an output signal from the input signal and processing circuitry for influencing the input signal based on a determined statistical value of the output signal. Furthermore, one or more example embodiments relates to a photon counting X-ray imaging system including such an X-ray detection system. Additionally, one or more example embodiments relates to a computed tomography device and a method of processing a signal.

In general, the task of photon counting systems for medical X-ray imaging, but also of other particle detectors, is to detect and count pulses generated by the registered particles and typically also to determine their energy. For this purpose, a sensor material (e.g. CdTe, CdZnTe, Si, . . . ) is used in direct converting detectors, for example, in which electron/hole pairs are generated when the photons are absorbed. With the help of a depletion voltage (also: bias voltage), the electron/hole pairs are separated and directed to opposite electrodes of the sensor. This influences a current signal on the electrodes, which is typically detected by an electronic circuit on the side of the pixelated electrode. This amplifies the charge pulses, performs pulse shaping if necessary and then compares the signal with at least one comparator. Each X-ray quantum thus generates a short current pulse when absorbed in a direct-converting sensor, the size/total charge of which is proportional to the energy deposited.

When the set comparator threshold is exceeded, the photon is finally detected and counted. At the same time, the minimum energy that a photon must have in order to be detected is determined by the choice of threshold. The energy of the detected photon can be determined in particular by using several comparators with different thresholds.

As the sequence of the X-ray quanta is random, overlapping of the individual pulses (so-called “pileup”) occurs more frequently, especially at high flux. This raises the specific technical problem of making the energy classification of the pulse measurement as stable and robust as possible over a wide range of possible X-ray fluxes. Applying the depletion voltage to the sensor material results in a leakage or dark current even without incoming photons. This depends on various parameters (sensor material, electrode types and materials, thickness of the sensor, voltage difference, temperature, current and previous radiation intensity, etc.) and is typically subject to slow fluctuations. With transimpedance amplifiers, this low-frequency signal component would shift the output signal of the amplifier, which would lead to a shift in the detected photon energies if the comparator thresholds remained unchanged, and must therefore be compensated for. With charge-sensitive preamplifiers, a change in the leakage current leads to suboptimal compensation and thus also to a distortion of the detected photon energy or even to saturation of the amplifier. If a photon flux is present, the actual signal is superimposed on the dark current. In the case of individual pulses with a sufficient time interval, each pulse would start on the baseline (the resting state without pulses) and return there completely. The pulse height and thus the photon energy could thus be determined correctly. However, as the photon flux increases, the low-frequency signal component also increases, which makes it difficult to compensate only for the dark current. Furthermore, the pulses overlap more and more frequently, i.e. they overlap (so-called pile-up case) and can be recognized as photons with higher energy. As a result, the count rate spectrum, which represents the counting events per time as a function of photon energy, is erroneously shifted in relation to the energy spectrum of the X-ray source as a function of the photon flux. The random sequence of the X-ray quanta therefore leads to increased superposition of the individual pulses due to pileup, particularly at high flux. This raises the specific technical problem of making the energy classification of the pulse measurement as stable and robust as possible over a wide range of possible X-ray fluxes. Particularly in the field of medical X-ray imaging, and even more particularly in computed tomography, the photon flux can change rapidly, i.e. from one measurement interval to the next, if a different area of the target with different absorption properties is scanned. If the baseline of the signal is then not adapted quickly enough to the changed photon flux, this also leads to falsified measurement results. The following problem arises when correctly determining the photon energy:

In many typical implementations, the problem remains unsolved or is only partially addressed.

For example, the sensor leakage current can be determined before the actual X-ray measurement and then compensated for by an adjusted static current at the input node (“static leakage current compensation”).

Alternatively, the compensation current can also be slowly adjusted dynamically (“dynamic leakage current compensation”), for example using a resistive feedback amplifier with a suitable transfer function. In this case, it makes sense for the feedback path to start after the first amplifier, thus ensuring that the output signal remains within its dynamic range. The feedback path typically contains a resistive (R) as well as a capacitive path (C) or a more complex impedance network (e. g Krummenacher feedback, Self-Cascoded FET with pole-zero cancellation (compare e.g. WO2024086081A). Depending on the configuration of R and C, the amplifier is then referred to as a transimpedance amplifier (R determines gain, C negligibly small, “TIA”), as a charge-sensitive amplifier (R almost infinite, C determines gain, “CSA”), as a charge-sensitive amplifier with continuous reset (R large, controls reset time constant, C determines gain). The transition between the types is continuous and there are also sensible mixed forms (R small enough to determine the gain, C large enough to ensure a certain charge collection time). Generally speaking, then, it is simply the feedback impedance that determines the transfer function of the amplifier, and in particular the low-frequency part of the transfer function provides compensation for the incoming sensor leakage current.

The energy classification is often only designed for the low-flow case. In this case, all pulses start from a known rest position and the maximum height above the rest position is a measure of the energy of the pulse. Deviations due to pileup are then often addressed by downstream numerical corrections (e.g. linearity corrections or spectral beam hardening corrections).

One possibility is the use of bipolar pulse shaping, in which a downstream undershoot compensates for the positive signal pulse. In this case, the net shift of the rest position is zero, so that the energy levels are briefly disturbed by other pulses, but not systematically shifted.

A dedicated circuit element, a so-called baseline restorer (BLR) or baseline holder (BLH), is usually implemented in particle detectors for dynamic adjustment of the signal baseline. A topology consisting of a preamplifier with a downstream (and capacitively isolated) pulse shaper is often found in photon counting. In this case, the BLH/BLR is necessary in order to establish a defined output level at all.

The baseline restorer (BLR) detects pulse-free times and pulls the signal to the desired baseline during these times. To be able to do this, it usually has a high bandwidth. Particularly in applications such as medical X-ray imaging with sometimes high photon fluxes, phases without pulses can be correspondingly rare and difficult to detect. For this reason, the use of a BLR in applications with long-term high photon fluxes is only suitable to a limited extent.

In contrast to the BLR, the baseline holder (BLH) is characterized by a low bandwidth and filters the low-frequency components out of the signal in order to then compensate for them. The typical BLH architecture is such that the difference between the amplified and pulse-shaped signal and the desired baseline is first amplified and, if necessary, processed with a non-linear function. The result is then low-pass filtered and converted into a current, which is then fed into the detector input for compensation.

Without using a non-linear function, the running average value of the signal is basically determined and compensated. This behavior corresponds to the AC coupling of the signal. As a result, the average value of the signal is also compensated at higher photon fluxes.

A different behavior is achieved if a non-linear function is applied to the differential voltage between the signal and the desired baseline. In the case of unipolar pulses, for example, the signal components below the baseline are weighted much more heavily than the components above. This can be realized, for example, by limiting the slew rate, which is only effective in one direction. Such non-linear behavior shifts the signal in such a way that the negative peak values are located on the baseline. This BLH behavior is also referred to as DC-coupled and essentially only compensates for the dark current.

AC-like coupling, in which the integral of the deviation of the output signal from the target value is regulated to zero. The aim here is for the average deviation to be zero, very similar to a bipolar pulse shape. In contrast to this, unipolar pulses can also be used with the baseline holder variant and the time constant of the reaction can be selected as required. With an intermediate pulse shape (proportional undershoot), the feedback effect is divided proportionally between the pulse shape and the baseline holder. Feedback with a certain time constant and with a reaction strength proportional to the deviation (RC-like behavior). The response strength and time constant can be set here, but a compromise must be made between the influence of high signal pulses and the feedback strength in the case of high flux. Large pulses are changed more than smaller pulses. Furthermore, the severity of the pulse-height-dependent influence depends on the current strength of the signal flow/pileup level. In combination, these two factors undermine the robustness of the energy classification. Feedback with a constant current strength so that the signal returns to the base line with a constant, signal independent slope, thereby causing a triangular pulse shape. This has the advantage of a predictable, pulse-height-independent effect on the signal pulses. However, it also causes a time-varying shift in the energy scale. In addition, the time until the return to the rest position depends linearly on the level of the previous deflection and does not have a uniform time constant. Asymmetrical response to overshoot or undershoot of the target voltage, in particular with low response to overshoot during signal pulses (e.g. using a large R), but strong response to undershoot of the target voltage (e.g. using a diode). The aim here is to ensure a minimum output level, which is set in particular as soon as a useful signal is no longer present, while at the same time minimizing the influence on the pulses in the event of a signal. The disadvantage is that a shift in the energy scale caused by pileup is hardly or not at all compensated. This type is very similar to a baseline restorer in the way it works. The various baseline holders therefore differ in particular in their response behavior. Known types are

One or more example embodiments provides stable and robust X-ray detection.

According to one or more example embodiments this is solved by an X-ray detection system and a method of processing a signal as set out in the independent claims. Further, preferable developments are defined in the subclaims. Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.

In one aspect, there is provided an X-ray detection system comprising a detector unit for detecting X-ray photons and for generating an input signal based on the detected X-ray photons and an advantageous signal processing device for processing the input signal.

An advantageous signal processing device comprises input means for receiving an input signal and signal processor for generating an output signal from the input signal. The signal processing device transforms the input signal to an output signal. The input means is capable of receiving the input signal. For example, the input means is realized by an interface which receives the input signal from an external unit. The external unit in case of the above-mentioned X-ray detection system is the respective detector unit capable of detecting X-ray photons and of generating the input signal based on the detected photons. The input signal generated by the detector unit is then received by input means of the signal processing device. The external unit in other applications may be, for example, a memory unit or a data network. The input means may comprise one or more memory units.

The signal processor for generating an output signal from the input signal may include an amplifier for amplifying the input signal. Furthermore, the signal processor optionally includes a shaper for shaping the amplified input signal, thus obtaining the output signal.

Furthermore, the signal processing device comprises the processing circuitry for influencing the input signal. E.g. the processing circuitry is capable of varying the offset or adding current to the input signal.

Furthermore, the processing circuitry is capable of determining a statistical value of the output signal. The statistical value may relate to pulses of the output signal. Furthermore, the processing circuitry is capable of comparing the statistical value with a pregiven setpoint value. In other words, the actual statistical value is compared with a target value. Additionally, the processing circuitry is capable of influencing the input signal such that the difference between the statistical value and the setpoint value in the output signal is reduced. For instance, the offset of the signal is varied in such a way that the difference between both values is minimal.

For instance, the output signal differs from the input mainly in terms of amplification (and shaping). The output signal can also have a completely independent offset. However, the value of the output offset can be influenced by changing the input offset. This enables a control loop to minimize the statistical characteristic in the output by controlling the offset on the input.

Advantageously, the input signal is optimized in relation to a specific statistical value by simply changing the offset of the input signal.

The detector unit comprised by the X-ray detection system may comprise a sensor, e.g. comprising CdTe, CdZnTe, Si, . . . as sensor material in case of a direct converting detector. In response to an absorbed photon within the sensor, a current signal is influenced at the sensors' electrodes, representing the input signal to an electronic circuit for processing the signal, which is connected in terms of signaling to the sensor. Such an electronic circuit, e.g. implemented as ASIC (application specific integrated circuit), may comprise the signal processing device as described above, i.e. the signal processing device and its means for processing and controlling the input signal received by its input means may be implemented in the electronic circuit in form of circuitry (also referred to as an input circuit). Further, the sensor as well as an electronic circuit for processing the signal from the sensor may be pixelated to allow for spatially resolved photon detection the sensor, e.g. by providing a pixelated electrode at least at one side of the sensor, especially the side of the sensor facing the electronic circuit in terms of signaling, and the electronic circuit by providing pixelwise signal processing. Thus, the signal processing device of the X-ray detection system may be provided for each pixel of a detector unit individually. There might as well be other implementations. Besides the proposed signal processing device such an electronic circuit as described above may comprise further analog or digital circuitry to process the received signal. In particular, a number of comparators and associated counters may be provided so that photon counting and, in particular, by providing a plurality of comparators, energy-resolved measurement of the detected photons is possible.

According to an embodiment of the present invention, the statistical value is a quantile (or mean value, median or other statistical moment) related to the output signal. The quantile (used below as a representative of all the statistical values mentioned) can be used to describe the probability that the output signal is below a certain (energy) threshold. For example, the pregiven setpoint value is defined as 30% quantile. In this case, the output signal is shifted by the influencing means (offset is varied) so that the statistical value of the output signal is shifted towards the pregiven 30% quantile. Thus, the quantile of the output signal can be adapted by varying the offset.

According to a further embodiment, the output signal is a continuous signal, and the quantile refers to a proportion of time during which the output signal is below a predetermined baseline. In this case, the quantile relates to the relative proportion of time in which the output signal is lower than a predefined threshold called baseline. This relative time below baseline is briefly referred to as TBB. The output signal may be an analogue or a digital signal. In either case TBB can be calculated with respect to a specific baseline.

In a further embodiment, the input signal comprises a pulse signal. Specially, the pulse signal can be regarded as pulse train. For example, the pulse signal is composed of a plurality of impulses. The input signal may comprise further signal components (e.g. noise, leakage etc.). The impulses may appear randomly. E.g. the input signal, namely the pulse signal, results from detecting X-ray photons. Thus, the pulse signal can be used for counting X-ray photons.

In another embodiment, the signal processor includes a charge sensitive amplifier or a transimpedance amplifier for amplifying the input signal. The charge sensitive amplifier converts electrical charges into a respective voltage. In contrast to that, the transimpedance amplifier converts a current into voltage. Both amplifiers can be implemented with one or more operational amplifiers.

According to a further embodiment, the processing circuitry is capable of adding a compensation current to the input signal, wherein the compensation current is being based on an output of the respective amplifier. Thus, a feedback loop can be realized. Specifically, the input signal is amplified by the charge sensitive amplifier or the transimpedance amplifier, and the compensation current is generated on the basis of the amplified signal. Finally, the compensation current is added to the input signal, thereby completing the loop. Thus, respective feedback control can be realized.

According to still another embodiment, the compensation current is generated by a baseline holder circuit (in short: baseline holder) or a baseline restorer circuit based on the output signal of the respective amplifier. As defined above, the baseline holder has a relatively small bandwidth and filters out low frequency components of the output signal from the respective amplifier in order to compensate for them. In contrast, the baseline restorer circuit detects pulse-free times and pulses the signal to the desired baseline during these times. The baseline restorer circuit usually has a much higher bandwidth than the baseline holder. Thus, the baseline used for determining the TBB can be influenced by the baseline holder circuit or the baseline restorer circuit.

According to another embodiment, the baseline holder comprises as concrete implementation of the part of the processing circuitry for determining the statistical property of the output signal two adjustable current sources of opposite polarity and independent strength for providing one current to an integrator for generating the compensation current, (only) while the output signal is below a pregiven baseline, and for providing the other current of opposite polarity to the integrator for generating the compensation current, (only) while the output signal is above a pregiven baseline. Specifically, the baseline holder circuit may comprise an integrator circuit and two adjustable current sources of opposite polarity connected to an input of the integrator. An output from the integrator is a basis of the compensation current, wherein one of the adjustable current sources provides current only if the output signal is below a pregiven baseline, and the other one of the adjustable current sources provides current only if the output signal is above the pregiven baseline. This means that the compensation current is generated on the basis of the positive and/or negative current provided to an integrator by the adjustable current sources. In other words, the positive and negative current do not represent the compensation current, but they are used for generating the compensation current.

The adjustable current sources can be implemented in various ways, e.g. by a series of optionally switchable partial current sources of different current strengths (e.g. powers of 2) or by potentiometers, etc.

The integrator is used for integrating the currents from the two adjustable current sources, wherein the output from the integrator is a basis of the compensation current. Usually, the integrator integrates the currents and provides a respective voltage. Such voltage has to be converted into the compensation current. A respective V/I converter may be provided. Thus, the integrator integrates the positive current as long as the output signal of the output means of the signal processing device is below the baseline, and it integrates the negative current as long as the output signal of the output means is above this baseline. Thus, the compensation current reduces the distance from the pregiven baseline.

In another embodiment, a current strength of one of the adjustable current sources of opposite polarity is proportional to the proportion of time during which the output signal is above the predetermined baseline, and a current strength of the other one of the adjustable current sources is proportional to the proportion during which the output signal is below the predetermined baseline. E.g. the positive current is proportional to the proportion of time of the input signal above the predetermined baseline, and the negative current is proportional to the proportion of time of the input signal below the predetermined baseline. In case the proportion (e.g. TBB) is small, a high positive current and a relatively small negative current are provided. Otherwise, if the proportion is high, a relatively small positive current and a relatively high negative current are provided. Thus, the absolute values of both currents have the required relation of (1−TBB)/TBB.

In another example embodiment of the present invention there is provided a photon counting X-ray imaging system including an X-ray detection system as described above, wherein the input signal comprises a respective pulse signal, and a counting unit for counting pulses of the output signal, which exceed a predetermined energy threshold. Thus, reliable photon counting can be performed with the aid of the above-described signal processing device.

In particular, a counting unit may comprise, e.g., at least one comparator and an associated counter to count pulses exceeding an energy threshold associated with the comparator. In particular, in a pixelated X-ray detection system, each pixel may be associated with or comprise at least one counting unit.

Based on the data of the counting unit an image can be generated by an image generation unit. Advantageously, high quality images can be obtained.

The counting unit may be capable of providing count rate values determined for several energy levels of the X-ray photons, e.g. by comprising a plurality of comparators with associated energy thresholds and counters. Furthermore, the counting unit may be capable of providing the count rate values in dependence of a flux of the X-ray photons. Specifically, the count rates may vary with the flux of the X-ray photons. Moreover, the counting unit may be capable of providing a spectral curve of the count rate values. Thus, the counting unit may provide a set of spectral curves of the count rate values over photon energy as a function of the flux of the X-ray photons or a set of flux curves of the count rate values over the flux of the X-ray photons (or tube current) as a function of photon energy.

The above object is also solved by a photon counting X-ray imaging system as described above, wherein the setpoint value of the processing circuitry is adjustable, and the counting unit is capable of providing a flux-dependent count rate response, so that spectral characteristics of the flux-dependent count rate response are adjustable with the setpoint value of the processing circuitry. The setpoint value represents a target point for the statistical value. In other words, the setpoint value is used to influence the spectral characteristics of the flux-dependent count rate responses (linearity curves). Specifically, the position of the spectral characteristics may be varied by changing the setpoint value.

According to a further embodiment, the setpoint value of the processing circuitry is adjusted, so that a flux dependent shift of features in the spectral characteristics is minimized. For instance, a local maximum of the spectrum changes its position as a function of the flux (e.g. the peak height of the output pulses corresponding to a certain characteristic line in the input X-ray spectrum can increase at higher fluxed due to pile-up with other concurrent pulses). This dependency from the flux can be reduced by choosing a proper setpoint value.

According to a further example embodiment of the present invention there may be provided a computed tomography device comprising a photon counting X-ray imaging system as described above. Thus, also CT-devices may benefit from the advantages of the inventive photon counting X-ray imaging system (e.g. through a reduced flux-dependency of the energy scale, through flux-independent contrast and/or through flux-independent Hounsfield-units).

receiving an input signal, determining an output signal from the input signal, determining a statistical value from the output signal, determining an input signal modification (e.g. offset) which reduces or minimizes a difference between the statistical value and a setpoint value. The above object is also solved by a method of processing a signal, the method comprising the steps:

receiving an input signal from the detector unit by the input means of the signal processing device, determining an output signal from the input signal by the signal processor of the signal processing device, determining a statistical value from the output signal by the processing circuitry of the signal processing device, determining an input signal modification which reduces the difference between the statistical value and a setpoint value by the processing circuitry of the signal processing device, and applying the input signal modification on the input signal by the processing circuitry. In particular, the above object is solved by a method of processing a signal using an X-ray detection system as described above, the method comprising the steps:

Usually, this reduction of the difference in the statistic characteristic only becomes visible with an updated output signal.

The advantages and further developments of the signal processing device, the X-ray detection system, the photon counting X-ray imaging system, and the computed tomography device also apply to the inventive method. The above described functional features of the respective devices can be seen as corresponding method features.

Furthermore, there may be provided a computer program or a computer-readable medium comprising instructions, which, when the program is executed by a signal processing device as described above, cause the signal processing device to carry out the above-mentioned method.

The following embodiments represent preferred examples of the present invention.

1 FIG. 1 1 2 3 11 2 3 2 3 3 shows a schematic representation of an advantageous embodiment of a proposed X-ray device as a medical CT (computed tomography) device. The CT devicemay comprise the X-ray source, a photon-counting X-ray detector comprising a detector unitand a processing unitas a kind of signal processing device. The signal processing device and the detector unit are shown separately here. In advantageous variants, however, these are implemented in the immediate vicinity of each other. In particular, the signal processing device may be comprised by an electronic circuit, for example in the form of an ASIC, which is connected to the detector unit. The X-ray sourceand the X-ray detector unitmay be arranged in opposition to each other. The X-ray sourcemay be configured to illuminate the X-ray detector unitwith X-rays along an X-ray incidence direction. The X-ray detector unitmay comprise a direct-conversion (semiconductor) X-ray detector layer as sensor layer. For example, the X-ray detector layer may comprise CdTe, CdZnTe, CdTeSe, CdZnTeSe, CdMnTe, Si, GaAs or Cr:GaAs as semiconductor material.

1 4 5 2 3 5 5 5 5 6 The CT devicecan also comprise a gantrywith a rotor. The X-ray sourceand the X-ray detector unitcan be arranged in a defined arrangement on the rotor, in particular integrated into the rotoror attached to the rotor. The rotorcan be mounted to rotate about an axis of rotation.

7 8 6 4 11 1 7 11 3 9 10 11 9 10 10 The examination objectto be imaged can be mounted on the patient positioning deviceand can be moved along the axis of rotationthrough the gantry. The processing unitcan be used to control the CT deviceand may comprise an image generation unit to calculate sectional images or volume images of the examination object. The processing unitmay comprise a counting unit for counting pulses generated by the detector unitwhen detecting X-ray photons. In advantageous variants, however, the counting unit can also at least in parts be comprised by an electronic circuit as mentioned above, which is connected to and in immediate vicinity to the detector unit. An input device, for example a keyboard, and an output device, for example a screen and/or display, can be connected to the processing unit, in particular coupled by signal technology. The input devicecan advantageously be integrated into the output device, for example in the case of an input display, in particular a resistive and/or capacitive input display. The output devicecan be designed to display a graphical representation of the counting signals and/or the X-ray image data set.

The schematic representations contained in the figures described do not depict any scale or proportions.

3 A further example (not shown in the figures) may relate of a monoplane X-ray system with a C-arm held by a stand in the form of a six-axis industrial or articulated robot, at the ends of which an X-ray radiation source, for example an X-ray source with X-ray tube and collimator, and an X-ray image detector as the detector unitare attached as an image acquisition unit. The realization of the X-ray diagnostic device is not dependent on the industrial robot. Conventional (fixed or movable) C-arm devices can also be used.

In this example a patient or a technical object to be examined may be positioned on a table top of a patient positioning table in the beam path of the X-ray emitter. A system control unit with a computer for image processing is connected to the X-ray diagnostic device, which receives and processes the image signals from the X-ray image detector. The system control unit may comprise a photon counting X-ray imaging system and/or a signal processing device as described above.

The X-ray images can then be viewed on the displays of a monitor light. The monitor light can be held by means of a ceiling-mounted, longitudinally movable, pivotable, rotatable and height-adjustable support system with a cantilever and lowerable support arm. A counting unit for counting X-ray pulses may also be provided in the system control unit.

11 In a specific embodiment the signal processing unituses a baseline holder (BLH) as processing circuitry with a quantile-based setting to compensate for a dark current and to achieve a photon flux-independent position of the count rate spectrum. The basis for controlling the BLH is the distribution function, which describes the probability that the signal is below a certain energy threshold. Preferrably, the BLH continuously determines this percentage of the signal below a baseline (the Time Below Baseline, TBB) and shifts the signal so that this percentage corresponds to a set quantile value. For example, if a 30% quantile is set, the signal is shifted so that it is 30% of the time below the baseline. The baseline itself is typically selected to correspond to an energy of 0 keV.

2 FIG. 3 12 12 13 14 14 13 The flow chart ofshows a possible signal processing of a signal of an X-ray detector unit. This signal is called input signal IS here. The input signal IS is a time variant pulse signal, usually. The input signal is fed to the positive input of a substractor(or with a negative sign to an adder). Alternatively, the polarities of the signals can be reversed at muliple points in the circuit without altering the scope of the invention. The label “positive”/“negative” are used here to provide a self-consistent explaination, without being limited to this specific choice of polarity set. The output of the substractoris provided to an amplifier, which amplifies the signal. The amplified signal may optionally be fed to a shaperin order to shape the pulses of the pulse signal. As a result, an output signal OS is provided at the output of the shaperor the amplifier. Alternatively, the amplifier might feature intrinsic shaping functionality so that no subsequent shaper is needed and the output signal OS is directly provided by the amplifier.

15 12 13 15 The output signal OS is fed to the baseline holderwhich produces a compensation current CC. The compensation current CC is provided to the negative input of the substractor. Thus, the compensation current CC is subtracted from the original input signal IS. The difference signal is provided to the amplifier. This means that there is provided a feedback loop wherein the baseline holderfeeds back the output signal OS in processed form to the input signal IS.

15 16 16 The baseline holdercomprises a comparator. The comparatorcompares the output signal OS with a baseline BL, which may be provided externally. Specifically, the baseline BL may be set manually via an interfce.

16 17 17 18 18 19 19 The output of the comparatoris fed to a weighting unitfor quantile based weighting. The output of the weighting unitis input to an integratorwhich integrates the signal. The output of the integratoris supplied to a voltage current converter. This voltage current converterproduces the compensation current CC from the integrated signal.

16 15 19 As described above, the input signal IS is first amplified and optionally pulse-shaped. The comparatorof the BLHcompares the amplified/pulse-shaped signal with a reference, a baseline voltage BL, and only outputs in binary form whether the signal is currently above or below this baseline. These two phases are then weighted according to the selected quantile: phases below the baseline are weighted in relation to phases above the baseline with the factor (1−TBB)/TBB. To set a 30% quantile, for example, a factor of 0.7/0.3=2.333 would be necessary with TBB=0.3. The weighted signal is finally integrated to obtain a control voltage, which is converted into the compensation current CC by means of the voltage/current converterand fed into the detector input, e.g. by adding it to or subtracting it from the input signal IS.

3 FIG. 20 16 17 21 22 16 21 18 18 22 18 A concrete implementation example of the BLH concept described is shown in. A limiting differential amplifier, for example, can serve as the comparatorhere. Weighting is carried out by the weighting unitcomprising two current sourcesandof different polarity, whose absolute values have the required ratio (1−TBB)/TBB to each other and are active alternately according to the output signal of the comparator. If the output signal OS is below the baseline BL (state “0”), the current sourceconnected to VDD is switched to the integratorin order to feed positive current to the integrator. In this state “0” the other current sourceconnected to ground is decoupled form the integrator.

22 18 18 21 18 Otherwise, if the output signal OS is above the baseline BL (state “1”), the current sourceconnected to ground is switched to the integratorin order to feed negative current to (draw current from) the integrator. In this state “1” the other current sourceconnected to VDD is decoupled form the integrator.

23 18 18 24 The respective current is then fed to a differential amplifierconnected as an integrator to form the integrator. The output voltage of the integratoris converted into the compensation current CC using a resistor, for example.

21 22 If the current sources,are kept configurable, a wide variety of quantiles can be selected for control.

While the desired quantile is set by the ratio of the two currents, the speed of the regulation can also be set independently of this by selecting a suitable average current I/2 and the integration capacitance Cintegr so that it matches the requirements of the application.

1 FIG. Other implementations of the BLH concept described are possible, as various circuits can be used for the different components shown in. For example, transistors can also be used as voltage/current converters. In the simplest case, the integrator can consist of just a single capacitor.

Even much more complex implementations are theoretically conceivable, e.g. the use of a time-to-digital converter, which converts the duration of both comparator states into digital values and carries out further processing (weighting, integration) in the digital domain.

Such signal processing allows for making the energy classification of the pulse measurement as stable and robust as possible over a wide range of possible X-ray fluxes.

The signal baseline does not have to be visible, as required by the function of a BLR, for example. This means that its use is not limited to applications with low photon fluxes. In the low flux case, the signal baseline is regulated to the desired reference baseline, regardless of the selected quantile. This means that the described BLH always behaves very similarly to a BLH with DC- or AC-coupled behavior in the low flux case and practically only compensates for the dark current. In the case of higher photon fluxes, the BLH setting, the selected quantile, defines the direction and strength of the shift in the count rate spectrum. A suitable choice of quantile (e.g. based on calibration measurements) can ensure that the position of the count rate spectrum is practically independent of photon flux for the given input signal spectrum. Conventional BLHs with DC- or AC-coupled behavior cannot achieve this. Due to the photon flux-independent position of the count rate spectrum, the BLH is particularly suitable for applications (such as medical X-ray imaging) in which high or strongly fluctuating photon fluxes can occur. The quantile-based setting is particularly suitable for simple realization. This is the case because the mode of operation is based solely on a ratio of two variables (e.g. two current sources) and can therefore be configured very easily and implemented independently of the process, voltage and temperature. The reaction speed of the described BLH to changes in the photon flux can be freely adjusted independently of the selected quantile. This allows it to be easily adapted to the requirements of the field of application. In the field of medical X-ray imaging, for example, it can be selected so that an adjustment is made within a measurement interval. The possibility of an adjustable/configurable quantile means that the BLH can be adapted to different pulse shapes and amplifier topologies. The selectable quantile can also be used to achieve a desired flow-dependent shift of the energy scale in the positive or negative direction. This can be used in particular to improve the linearity behavior (at the expense of energy stability), since higher energy thresholds paralyze later. Various advantages result from using of a BLH with quantile-based adjustment and its circuit realization:

4 5 FIGS.and The main advantage of this concept is therefore that it can be used to achieve an almost flux-independent stabilization of the energy scale. For use in computed tomography, this means that the measured contrasts and HU values are independent of flux. This is a key requirement for quantitative CT imaging. This advantage is shown in.

4 FIG. 25 26 25 26 27 28 shows sections of differential count rate spectra for different fluxes of X-ray photons. The higher the flux, the higher the counts (i.e. the respective spectrum). The spectra (here also called spectral characteristics) have two exemplary spectral features, namely a first local maximumand a second local maximum. The higher the flux, the more the respective local maximum,is widened or smaered and the further it is shifted to the left towards smaller energy. However, the shift can also be to the right towards higher energy. The shift can be easily recognized with respect to vertical dotted linesand. The shift can be compared to the fact that the color of an image changes with increasing brightness. However, this is undesirable.

5 FIG. 25 26 27 28 As shown in, the inventive method is capable of stabilizing the spectral features. For instance, the local maximaandare kept constantly on the vertical linesandeven with increasing flux. This can be obtained by adjusting the quantile respectively. The spectra or spectral features do not show an energy dependency from the flux.

At the same time, a dynamic, automatic adaptation to the locally and temporally changing leakage currents of the individual pixels is achieved. On the one hand, this eliminates the need for interim leakage current calibration measurements.

On the other hand, it creates a detector system that is robust against changes in the sensor leakage current. This enables the spatial and temporal stability of the sensor signal required for CT imaging.

The concept described above thus represents an advantagous mean to make photon-counting imaging and especially photon-counting CT more reliable.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections, should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. The phrase “at least one of” has the same meaning as “and/or”.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below,” “beneath,” or “under,” other elements or features would then be oriented “above” the other elements or features. Thus, the example terms “below” and “under” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. In addition, when an element is referred to as being “between” two elements, the element may be the only element between the two elements, or one or more other intervening elements may be present.

Spatial and functional relationships between elements (for example, between modules) are described using various terms, including “on,“ ”connected,” “engaged,” “interfaced,” and “coupled.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the disclosure, that relationship encompasses a direct relationship where no other intervening elements are present between the first and second elements, and also an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. In contrast, when an element is referred to as being “directly” on, connected, engaged, interfaced, or coupled to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the terms “and/or” and “at least one of” include any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Also, the term “example” is intended to refer to an example or illustration.

It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It is noted that some example embodiments may be described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented in conjunction with units and/or devices discussed above. Although discussed in a particular manner, a function or operation specified in a specific block may be performed differently from the flow specified in a flowchart, flow diagram, etc. For example, functions or operations illustrated as being performed serially in two consecutive blocks may actually be performed simultaneously, or in some cases be performed in reverse order. Although the flowcharts describe the operations as sequential processes, many of the operations may be performed in parallel, concurrently or simultaneously. In addition, the order of operations may be re-arranged. The processes may be terminated when their operations are completed, but may also have additional steps not included in the figure. The processes may correspond to methods, functions, procedures, subroutines, subprograms, etc.

Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The present invention may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

In addition, or alternative, to that discussed above, units and/or devices according to one or more example embodiments may be implemented using hardware, software, and/or a combination thereof. For example, hardware devices may be implemented using processing circuity such as, but not limited to, a processor, Central Processing Unit (CPU), a Graphics Processing Unit (GPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, or any other device capable of responding to and executing instructions in a defined manner. Portions of the example embodiments and corresponding detailed description may be presented in terms of software, or algorithms and symbolic representations of operation on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

It should be borne in mind that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” of “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device/hardware, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

In this application, including the definitions below, the term ‘module’ or the term ‘controller’ may be replaced with the term ‘circuit.’ The term ‘module’ may refer to, be part of, or include processor hardware (shared, dedicated, or group) that executes code and memory hardware (shared, dedicated, or group) that stores code executed by the processor hardware.

The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module.

Software may include a computer program, program code, instructions, or some combination thereof, for independently or collectively instructing or configuring a hardware device to operate as desired. The computer program and/or program code may include program or computer-readable instructions, software components, software modules, data files, data structures, and/or the like, capable of being implemented by one or more hardware devices, such as one or more of the hardware devices mentioned above. Examples of program code include both machine code produced by a compiler and higher level program code that is executed using an interpreter.

For example, when a hardware device is a computer processing device (e.g., a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a microprocessor, etc.), the computer processing device may be configured to carry out program code by performing arithmetical, logical, and input/output operations, according to the program code. Once the program code is loaded into a computer processing device, the computer processing device may be programmed to perform the program code, thereby transforming the computer processing device into a special purpose computer processing device. In a more specific example, when the program code is loaded into a processor, the processor becomes programmed to perform the program code and operations corresponding thereto, thereby transforming the processor into a special purpose processor.

Software and/or data may be embodied permanently or temporarily in any type of machine, component, physical or virtual equipment, or computer storage medium or device, capable of providing instructions or data to, or being interpreted by, a hardware device. The software also may be distributed over network coupled computer systems so that the software is stored and executed in a distributed fashion. In particular, for example, software and data may be stored by one or more computer readable recording mediums, including the tangible or non-transitory computer-readable storage media discussed herein.

Even further, any of the disclosed methods may be embodied in the form of a program or software. The program or software may be stored on a non-transitory computer readable medium and is adapted to perform any one of the aforementioned methods when run on a computer device (a device including a processor). Thus, the non-transitory, tangible computer readable medium, is adapted to store information and is adapted to interact with a data processing facility or computer device to execute the program of any of the above mentioned embodiments and/or to perform the method of any of the above mentioned embodiments.

Example embodiments may be described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented in conjunction with units and/or devices discussed in more detail below. Although discussed in a particular manner, a function or operation specified in a specific block may be performed differently from the flow specified in a flowchart, flow diagram, etc. For example, functions or operations illustrated as being performed serially in two consecutive blocks may actually be performed simultaneously, or in some cases be performed in reverse order.

According to one or more example embodiments, computer processing devices may be described as including various functional units that perform various operations and/or functions to increase the clarity of the description. However, computer processing devices are not intended to be limited to these functional units. For example, in one or more example embodiments, the various operations and/or functions of the functional units may be performed by other ones of the functional units. Further, the computer processing devices may perform the operations and/or functions of the various functional units without sub-dividing the operations and/or functions of the computer processing units into these various functional units.

Units and/or devices according to one or more example embodiments may also include one or more storage devices. The one or more storage devices may be tangible or non-transitory computer-readable storage media, such as random access memory (RAM), read only memory (ROM), a permanent mass storage device (such as a disk drive), solid state (e.g., NAND flash) device, and/or any other like data storage mechanism capable of storing and recording data. The one or more storage devices may be configured to store computer programs, program code, instructions, or some combination thereof, for one or more operating systems and/or for implementing the example embodiments described herein. The computer programs, program code, instructions, or some combination thereof, may also be loaded from a separate computer readable storage medium into the one or more storage devices and/or one or more computer processing devices using a drive mechanism. Such separate computer readable storage medium may include a Universal Serial Bus (USB) flash drive, a memory stick, a Blu-ray/DVD/CD-ROM drive, a memory card, and/or other like computer readable storage media. The computer programs, program code, instructions, or some combination thereof, may be loaded into the one or more storage devices and/or the one or more computer processing devices from a remote data storage device via a network interface, rather than via a local computer readable storage medium. Additionally, the computer programs, program code, instructions, or some combination thereof, may be loaded into the one or more storage devices and/or the one or more processors from a remote computing system that is configured to transfer and/or distribute the computer programs, program code, instructions, or some combination thereof, over a network. The remote computing system may transfer and/or distribute the computer programs, program code, instructions, or some combination thereof, via a wired interface, an air interface, and/or any other like medium.

The one or more hardware devices, the one or more storage devices, and/or the computer programs, program code, instructions, or some combination thereof, may be specially designed and constructed for the purposes of the example embodiments, or they may be known devices that are altered and/or modified for the purposes of example embodiments.

A hardware device, such as a computer processing device, may run an operating system (OS) and one or more software applications that run on the OS. The computer processing device also may access, store, manipulate, process, and create data in response to execution of the software. For simplicity, one or more example embodiments may be exemplified as a computer processing device or processor; however, one skilled in the art will appreciate that a hardware device may include multiple processing elements or processors and multiple types of processing elements or processors. For example, a hardware device may include multiple processors or a processor and a controller. In addition, other processing configurations are possible, such as parallel processors.

The computer programs include processor-executable instructions that are stored on at least one non-transitory computer-readable medium (memory). The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc. As such, the one or more processors may be configured to execute the processor executable instructions.

The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language) or XML (extensible markup language), (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective-C, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5, Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, and Python®.

Further, at least one example embodiment relates to the non-transitory computer-readable storage medium including electronically readable control information (processor executable instructions) stored thereon, configured in such that when the storage medium is used in a controller of a device, at least one embodiment of the method may be carried out.

The computer readable medium or storage medium may be a built-in medium installed inside a computer device main body or a removable medium arranged so that it can be separated from the computer device main body. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium is therefore considered tangible and non-transitory. Non-limiting examples of the non-transitory computer-readable medium include, but are not limited to, rewriteable non-volatile memory devices (including, for example flash memory devices, erasable programmable read-only memory devices, or a mask read-only memory devices); volatile memory devices (including, for example static random access memory devices or a dynamic random access memory devices); magnetic storage media (including, for example an analog or digital magnetic tape or a hard disk drive); and optical storage media (including, for example a CD, a DVD, or a Blu-ray Disc). Examples of the media with a built-in rewriteable non-volatile memory, include but are not limited to memory cards; and media with a built-in ROM, including but not limited to ROM cassettes; etc. Furthermore, various information regarding stored images, for example, property information, may be stored in any other form, or it may be provided in other ways.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, data structures, and/or objects. Shared processor hardware encompasses a single microprocessor that executes some or all code from multiple modules. Group processor hardware encompasses a microprocessor that, in combination with additional microprocessors, executes some or all code from one or more modules. References to multiple microprocessors encompass multiple microprocessors on discrete dies, multiple microprocessors on a single die, multiple cores of a single microprocessor, multiple threads of a single microprocessor, or a combination of the above.

Shared memory hardware encompasses a single memory device that stores some or all code from multiple modules. Group memory hardware encompasses a memory device that, in combination with other memory devices, stores some or all code from one or more modules.

The term memory hardware is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium is therefore considered tangible and non-transitory. Non-limiting examples of the non-transitory computer-readable medium include, but are not limited to, rewriteable non-volatile memory devices (including, for example flash memory devices, erasable programmable read-only memory devices, or a mask read-only memory devices); volatile memory devices (including, for example static random access memory devices or a dynamic random access memory devices); magnetic storage media (including, for example an analog or digital magnetic tape or a hard disk drive); and optical storage media (including, for example a CD, a DVD, or a Blu-ray Disc). Examples of the media with a built-in rewriteable non-volatile memory, include but are not limited to memory cards; and media with a built-in ROM, including but not limited to ROM cassettes; etc. Furthermore, various information regarding stored images, for example, property information, may be stored in any other form, or it may be provided in other ways.

The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks and flowchart elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.

Although described with reference to specific examples and drawings, modifications, additions and substitutions of example embodiments may be variously made according to the description by those of ordinary skill in the art. For example, the described techniques may be performed in an order different with that of the methods described, and/or components such as the described system, architecture, devices, circuit, and the like, may be connected or combined to be different from the above-described methods, or results may be appropriately achieved by other components or equivalents.